---
title: fill() function
description: >
  `fill()` replaces all null values in input tables with a non-null value.
menu:
  flux_v0_ref:
    name: fill
    parent: universe
    identifier: universe/fill
weight: 101
flux/v0/tags: [transformations]
introduced: 0.14.0
---

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`fill()` replaces all null values in input tables with a non-null value.

Output tables are the same as the input tables with all null values replaced
in the specified column.

##### Function type signature

```js
(<-tables: stream[B], ?column: string, ?usePrevious: bool, ?value: A) => stream[C] where B: Record, C: Record
```

{{% caption %}}
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}

## Parameters

### column

Column to replace null values in. Default is `_value`.



### value

Constant value to replace null values with.

Value type must match the type of the specified column.

### usePrevious

Replace null values with the previous non-null value.
Default is `false`.



### tables

Input data. Default is piped-forward data (`<-`).




## Examples

- [Fill null values with a specified non-null value](#fill-null-values-with-a-specified-non-null-value)
- [Fill null values with the previous non-null value](#fill-null-values-with-the-previous-non-null-value)

### Fill null values with a specified non-null value

```js
import "sampledata"

sampledata.int(includeNull: true)
    |> fill(value: 0)

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z |         | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z |         | t1   |
| 2021-01-01T00:00:40Z |         | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z |         | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z |         | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | 0       | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 0       | t1   |
| 2021-01-01T00:00:40Z | 0       | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | 0       | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 0       | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}

### Fill null values with the previous non-null value

```js
import "sampledata"

sampledata.int(includeNull: true)
    |> fill(usePrevious: true)

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z |         | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z |         | t1   |
| 2021-01-01T00:00:40Z |         | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z |         | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z |         | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z | -2      | t1   |
| 2021-01-01T00:00:10Z | -2      | t1   |
| 2021-01-01T00:00:20Z | 7       | t1   |
| 2021-01-01T00:00:30Z | 7       | t1   |
| 2021-01-01T00:00:40Z | 7       | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z |         | t2   |
| 2021-01-01T00:00:10Z | 4       | t2   |
| 2021-01-01T00:00:20Z | -3      | t2   |
| 2021-01-01T00:00:30Z | 19      | t2   |
| 2021-01-01T00:00:40Z | 19      | t2   |
| 2021-01-01T00:00:50Z | 1       | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}